FP Gearbox: Last stage gear?

Technical Motors
1

Does anyone know the DP (or module) and pressure angle of the gears in the FP gearbox’s last stage (2009 model with the two blue final stages)? The pinion is a 12 teeth gear that our gear drawing software (GearTrax) can’t possibly match - odd shaped teeth which does not appear to be an integer DP or usual module.

Those two old threads from very respectable sources indicate 15DP and 16DP, but the 12 teeth gear I have in my hands is a log bigger than that - I believe those gearboxes have changed a bit over the past few years.

Any gear experts over here? :wink:

2

You can try measuring the diameter and counting the number teeth, you should be able to look up the pitch on a table at that point. I haven’t opened the new fisher prices so I don’t know off the top of my head.

3

Well, I gave it another shot, and the best I could measure the very last gear (38 teeth, with the extended plastic) is 2.25 module, 20 degrees pressure angle (nearly perfect match). The 12 tooth gear, the one I was interested in, does not appear to be the same, by a good margin, which is obviously very weird.

Since I’m not a gear expert, not even a mechanical guy, I’ll leave this one for the MEs out there. For our application, close enough was more than we needed, so we just drew the gear profile “by eye”, machined it on our home-made CNC mill, measured, and iterated - only took two shots! :wink:

4

Quick question I wanted to cnc gears on my cnc but what tools or bits would I need to get the job done?

Thanks in advance.

5

That will depend on the size of the gear and the material. The smaller the teeth, the smaller the cutter, I assume.

6

Normally this requires an involute gear cutter(or hob), of which there will be several for the same Diametrical Pitch value, as the profile of the cutter needs to change a bit due to the number of teeth. You can also grind a peice of tool steel to make a form tool and use it as a single point cutter. OR if the tooth profile is large enough, you can use a properly sized end mill to cut the gear on a 3 axis mill. However this would likely be a very hard thing to accomplish(in something other than plastic / wood), for reasons I wont go into here. So, if you have a 4 axis CNC or a manual mill with a dividing head, or rotary table look into the involute gear cutters.
If you want to search around some, another word for gear cutting is hobbing.
Here is one example


and here is another, using a different style cutter